This gold aluminum cover was designed to protect the Voyager 1 and 2 "Sounds of Earth" gold-plated records from micrometeorite bombardment, but also serves a double purpose in providing the finder a key to playing the record. The explanatory diagram appears on both the inner and outer surfaces of the cover, as the outer diagram will be eroded in time.
Flying aboard Voyagers 1 and 2 are identical records, carrying the story of Earth far into deep space. The 12-inch gold-plated copper discs contain greetings in 60 languages, samples of music from different cultures and eras and natural and man-made sounds from Earth. They also contain electronic information that an advanced technological civilization could convert into diagrams and images.
Image credit: NASA